1. Field
This document relates to a device and method of testing an internal resistance of a battery pack, and more particularly, to a device and method of testing the internal resistance of a battery pack used in an electric vehicle and a hybrid powered vehicle.
2. Description of Related Art
The battery pack plays an important role in electric vehicle and hybrid power vehicle. The battery pack system is generally coupled in series. Individual cells in the battery pack may become damaged and affect the entire capacity of the battery pack. That means, the entire capacity of the battery pack can be determined by one or more damaged cells. Accordingly, accurately measuring each cell state is necessary to avoid the failure of the battery pack.
At present, the testing method for the internal resistance of the battery pack includes a direct current discharge method and an alternating current injection method. The direct current discharge method includes generating an instant load current generated by a battery pack, measuring the instant change of voltage at the electrode pole of the battery pack, and calculating the internal resistance of the battery pack. This has several disadvantages. First, the remaining capacity must be measured and displayed frequently, which requires the frequent measuring of the internal resistance, and care must be taken so as not to influence the normal operation and reduce the remaining capacity of the battery pack.
Second, the number of the battery packs in the electric vehicle is large, and such measurement may waste a large portion of the capacity of the battery pack, and may be only suitable when a large load resistance is applied and measured with a high current scope or other device. If the battery pack current is measured with a low current scope or other device, it may not be properly loaded with the required large current of about several tens of amperes in short amount of time of several seconds. Accordingly, a large current passes through the battery pack, which may damage the electrodes in the battery pack and may adversely affect measurement accuracy. Further, this method may not be used with hybrid vehicles.
The alternating current injection method includes adding a constant alternating audio current source to two sides of the battery pack, detecting the voltage difference between the two sides of the battery pack, and detecting the phase difference therebetween. The internal resistance of the battery pack may be determined according to Ohms' law.
In the alternating current injection method, safely detecting the internal resistance of the battery pack online may be realized with no need to discharge the battery pack, which avoids affecting performance of the battery pack. However, similar to the problems associated with the direct current discharge method, the alternating current injection method has a limitation problem of the voltage scope of the detected battery pack. Moreover, the alternating current injection method needs to used a processor or master control unit (MCU) to calculate certain trigonometric functions. Thus, the hardware circuit and algorithm is complicated, which affects measurement accuracy.